Rats and mice are spontaneous ovulators – i.e. they do not need the presence of males to induce ovulation. There is some evidence the stimulation from male mice can induce and or/hasten ovulation and synchronize cycles in mice. Rats are mice typically have a 4-6 day cycle which consists of 4 stages – estrus, proestrus, diestrus I (a.k.a metestrus) and diestrus II.